It's a Bird, It's a Plane, It's... Oh No!

So
where's Superman when you need him?

By Lavinia Ponniah

Since the Shoemaker-Levy comet collision with Jupiter in July 1994, there has
been a rage of theories suggesting that the same devastating misfortune could
happen here on Earth. In response, the National Aeronautics and Space
Administration (NASA) has appointed a committee of scientists and astrophysicists
to plot all near-earth objects (comets and asteroids) that may threaten Earth
in
the next 10 years.

The Shoemaker-Levy comet, now in pieces, on its way to impacting
Jupiter.
(Shot from The Hubble Space Telescope)

Two thousand asteroids are estimated to exist with a diameter greater than 1
kilometer that are also due at some point to cross the orbit of Earth. This
makes the possibility of a collision, although remote, still very real.
Thankfully, these cosmic impacts only occur once every 200,000 years or so. Large
comets also pose a threat. When these comets are pulled towards the Sun it
breaks them up into a stream of debris. If these rather large particles of space
dust gather around earth's atmosphere, it could cause another Ice Age. An actual
collision with a comet's nucleus would also be cataclysmic.

[ Almost certainly, the
dinosaurs of 65 million years took the brunt of something big and awful that fell
from the sky. Dr. Frank Kyte, a geophysicist at the University of California at
Los Angeles, recently (November 1998) published a paper in the journal Nature
stating that he had found the very first physical evidence of this
dino-killing asteroid. It was a small coarse-grained fleck containing tell tale
ingredients of Iridium, and levels of iron, nickel, and chromium found only in
outer space. The specimen was found on the floor of the Pacific Ocean at just the point
where the Cretaceous period of massive dinosaurs transitions into the Tertiary epoch 65 million years ago. This
transition layer is known as the K/T boundary. This highly distinctive layer marks, it is
believed, the results of a gigantic amount of asteroid kicked-up debris that
eventually settled back to earth after annihilating impact. -- Ed.]

These past few years, the consequences of such a large-scale impact disaster have
been the focus of everything from religious cults to movie blockbusters. Between
them, the concept of Armageddon has been exploited to its fullest. There is,
however, a scientific basis for at least some of this hysteria. About 10 years
ago, in 1989, a cosmic boulder, just slightly bigger than an aircraft carrier,
passed within 400,000 miles of the Earth. This is a fairly close shave in
astronomical terms.

However, most astronomers seem more concerned about the collision between Earth
and the flying objects in the Taurid stream. The Taurid stream consists of cosmic
rubble and dust. This space borne debris travels at a break neck speed of 46,000
mph and swings through the Earth's orbit on biannual crossings.

Dr. Victor Clube of the Department of Astrophysics at Oxford University has
suggested that the 'megatonnage' explosion resulting from an impact with such
celestial objects would produce an immense amount of debris. It could block out
the sun for a considerable amount of time, throwing the world back into the Ice
Age. But Dr. Clube and his fellow scientists are as concerned about the atomic
solution suggestions in some "end of the world" movies, like "Deep Impact" and
"Armageddon." Shattering incoming asteroids or comets with nuclear weapons could
actually pose a greater danger to earth. Instead of one large threat, we will be
faced with a massive amount of space debris that would still throw Earth into
darkness on impact.

The Shoemaker-Levy comet impacting Jupiter.
Each small bright
impact flash is bigger than planet Earth!

There is also an "atomic bullet" targeting problem. According to a paper
published in Nature on June 4th, 1998, asteroids were mapped and found to be
multi-lobed. Thus, they were not so much like a solid rock but more like a gravel
pile loosely held together by fine dust. Therefore a single nuclear detonation
could be totally absorbed by just one lobe of the object. Hence, an atomic
explosion would likely not damage or deflect the asteroid as intended.

So how to defend ourselves? The first thing we have to do is find and precisely
locate the biggest potential threats. The most recent development in asteroid and
comet tracking has been achieved with the installation of new telescope pointing
and control software called the Lowell Observatory Near-Earth Object System
(LONEOS), installed at Lowell Observatory. LONEOS has now produced its first full
set of detailed images. Preliminary performance results suggest that LONEOS would
be able to survey about 10,000 square degrees of space each month.

The LONEOS telescope control program has been modified to accept pointing
directions from its camera control computer. A program that generates macros for
the camera control computer enables the telescope to take long sequence of images
without observer intervention. Using LONEOS, scientists at the Lowell Observatory
discovered the most recent Near-Earth object on 18 June 1998, called 1998MQ. At
first the object didn't seem to be moving and was ignored. Later, they discovered
that it had moved about 7 degrees north and appeared to be moving rather quickly.
This led to much discussion, and not more than a little excitement in the media.
Fortunately, it was a harmless event.

The fact is most asteroids and comets that are orbiting on an Earth-crossing
course have not been discovered yet. Even with modern systems like LONEOS it
will take more than a century to have mapped all of their locations. If Earth
were to
be on the receiving end of an asteroid or comet, we would have almost no warning
whatsoever. The only indication that something really bad had just come our way
would be a ground shattering explosion, supersonic shock wave and a blinding
blast of light, all too late. These unsettling facts serve to underscore a recent
suggestion by David Morrison, head of the Space Science Division at NASA Ames
Research Center in Mountain View, California. Morrison is urging that the only
way to successfully keep track of potentially dangerous asteroids is to install
at least six of the $12 million LONEOS telescopes throughout North and South
America. Until these additional systems are built, earth is flying almost
blind.

But even assuming we had a globally dispersed system that provided earth with
early impact detection and several months or more of warning what could we do
about it? One possible answer comes from NASA. In collaboration with The
Institute of Aeronautics and Astronautics (IAA), NASA is proposing to manufacture
power units that could attach themselves to celestial boulders and divert these
hazards away from Earth. One multi-million dollar effort researching the
feasibility of asteroid deflection is Clementine 2. This project involves
launching a satellite into a distant orbit that is equipped with high-speed
probes that can locate and "lock on" to asteroids. The probes then proceed to
strike the targeted objects at speeds of up to 40,000 mph. Each Clementine 2
probe has been designed to include sophisticated camera equipment to record the
deflective effect on the approaching asteroid.

Another method much discussed in scientific circles is using lasers to deflect
approaching asteroids. Asteroids and comets in space have devastatingly cold
temperatures on their surfaces. The atmosphere in space and the speed at which
the objects travel cause these extremely low temperatures. The idea is to use a
laser beam large enough to heat the surface of an approaching asteroid. The heat
created would then 'boil off' the asteroid. This is the same heating phenomenon
the asteroid would go through if it were to penetrate our atmosphere at high
speed. The thrust forces caused by escaping gases coming off the object's laser
heated surface should be large enough to change the orbit of the asteroid, but
only by a small amount. However, even a few degrees in course change may be
enough to change its collision path with earth.

But there are a few disadvantages with this laser heating method. If the heated
gases cause a deflection in the opposite direction as intended, that could turn a
near miss into a definite impact! Furthermore, laser beams, while nominally
parallel, may not be sufficiently so over tens of millions of miles. The great
distances involved would cause laser beam spreading which in turn reduces heat
concentration. Therefore, the only effective method for using lasers is at close
proximity. In addition, accurate aiming also poses a problem. More problems arise
when the laser beam has to target a moving object. The laser approach also needs
about 10-15 years to work effectively because of the lack of concentration of the
heat from the laser as it is transmitted over such a large distance in space.
Therefore the asteroid that becomes the target needs to be spotted many years in
advance And because the direction of thrusts from the expulsion of the gases from
the asteroid's surface cannot be predicted (because the asteroid is not of
uniform density and consists of lobes) it is also safer that the laser be used at
larger distances to prevent a near miss from becoming a definite impact.

One proposed idea for better targeting is to use a laser beam source
stationed in earth orbit that would work on objects which remained at a certain
'constant' distance from Earth. Even so, precautionary measures would need to be
taken to ensure the path the laser takes while shooting at the moving asteroid
does not cross the Earth's surface. Laser beams of such high power can cause
severe damage to the very planet it is trying to protect.

American Professor Jay Melosh and Russian professor Ivan Nemchinov have also
proposed launching a mirrored aluminum sail-like satellite into an orbit that
tracks dangerous asteroids. Their idea is based on the boy scouts method of
starting a fire using a magnifying glass to reflect and concentrate the Sun's
rays. Similar to a laser's effect, the reflective disc collects Sun rays, raises
them to approximately 2000 degrees in temperature, and focuses them onto a point
on the asteroid, hence vaporizing ice and rock from it's surface. But Melosh and
Nemchinov concede that, as with lasers, the lack of concentration of heat on the
object's surface also means long range advance information of approximately 10-15
years is absolutely vital for their machine to work. It will take that long for
the sun's rays to do their job.

Another idea to deflect earth-bent asteroids was developed by the Space Studies
Institute (SSI). They took the idea of the Clementine 2 power units developed by
NASA and IAA, and made a slight, but very significant modification. Instead of a
kamikaze probe that locked on and attacked the asteroid at high speeds, SSI's
probe would gently land on the asteroid, and then firmly attach itself. The
probe's mass driver engine would then produce the low, yet steady and continuous
thrust needed to gradually change the asteroid's course, using the asteroid's own
material for reaction mass.

The SSI design also heralds a new era when earth is no longer threatened with
extinction by asteroids, but instead benefits from them. The SSI mass driver
engine is also designed for drilling and mining on asteroids. Once the dangerous
object was shepherded into a High Earth Orbit and rendered safe, mining on the
asteroid would be carried out. This project holds the promise of obtaining vast
amounts of raw materials and resources in a manner not damaging to our
environment.